A power converter is a power supply or power processing circuit that converts an input voltage waveform into an output voltage waveform. Important characteristics of power converters are the ability to regulate accurately a characteristic of the output voltage waveform such as a dc voltage level, the ability to produce the output voltage waveform with a low level of ripple voltage, and the ability to execute the power conversion process with high efficiency. Power conversion efficiency is the ratio of power converter output power to input power.
Early designs of power converters generally employed dissipative regulators to regulate the output characteristic, which inherently produce a “quiet” voltage waveform without added ripple. However, more recent designs of power converters frequently employ a “switch-mode” circuit topology in place of a less efficient dissipative regulator. In a switch-mode power converter, a power switch is periodically turned fully on and fully off with a “duty cycle,” and operates in conjunction with reactive circuit elements such as inductors and capacitors to perform the power conversion function. Ideally, operating a power switch only in an on and off condition and the use of reactive circuit elements enables the design of a power converter with high power conversion efficiency. However, ripple components are produced at an input and an output of the power converter by the switching action of the power switch, which requires inclusion of a filter for their attenuation.
A filter is generally formed with further reactive circuit elements, i.e., inductors and capacitors, which contribute to power losses in the circuit. Losses in a power switch can generally be managed by providing a switch of suitable size, and by controlling simultaneous application of voltage and current to the switch during transitions between conducting and nonconducting states. But inductors and other magnetic circuit elements are generally formed with multiple layers of copper windings wound around dissipative core materials such as soft ferrites, and sustain power losses in the windings due to skin and proximity effects. Losses in magnetic circuit elements are managed by careful design of the winding geometry, choice of magnetic materials, and the physical size of conductors. Nonetheless, a significant challenge remains for a circuit designer to find a suitable design strategy for a magnetic circuit element with sufficiently low power dissipation characteristics for the more difficult applications.
Thus, despite the use of switch-mode power conversion circuit topologies and careful design of components used therein, market needs for the more challenging applications require further increases in the efficiency of a power converter beyond those presently being achieved. In accordance therewith, a filtering technique for a switch-mode power converter that provides a low level of ripple at an output thereof without incurring substantial power losses would be a beneficial improvement to meet these market needs.